problems OS 3.1 2g reboot

hi guys, sorry my first post is about problems, but this one is driving me crazy

i have an iphone 2g 8GB and recently updated to OS 3.1, that when my nightmare started every time i need to turn it off and on again, it get struck in the apple logo, its driving me crazy, im intally some apps on cydia, maybe that the source if the problem, dont know... i have try rebooting installing one by one, but always freeze at some point. so.. can anyone tell me if i have to downgrade to a lower versio or upgrade to 3.1.2 using blackra1n.. please help